addDays — GTM Variable Template for Date

VARIABLES › DATE

addDays EXTENDED Date

Direct (.tpl) Apply (.tpl) Add to GTM

Adds a given number of days to a date string and returns the new date in YYYY-MM-DD format.

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When to Use This

Date & Time

Calculate durations, differences, and time-based operations on date values.

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Examples

Add One Week▶ Try

INPUT

Target Date: 2024-04-20
Days to Add: 7

OUTPUT

2024-04-27

Cross Month Boundary▶ Try

INPUT

Target Date: 2024-04-30
Days to Add: 1

OUTPUT

2024-05-01

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Live Sandbox

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addDays

Read-Only Try Live

Target Date

💾 The starting date in YYYY-MM-DD format.

Supported formats:
  ✓ String

Days to Add

🔢 The number of days to add to the target date.

Input Setup

Input Function (optional)

⚙️ Optional pre-processing function applied to the input before internal logic (e.g., convert object to string, normalize case). Internal transformations such as case handling will still apply afterward.

Result Handling

Output Function (optional)

⚙️ Optional function to apply to the result before returning it (e.g., str => str + ' €', val => val !== undefined for boolean conversion). Useful for chaining transformations on the output.

Target Date string

💡 Type any text to see the result update live

🎯 Using special value — click input to type instead

Test with:

Falsy undefined null "" empty 0 false NaN

Truthy true 42 "hello" {} empty [] empty {a:1} [1,2,3]

Days to Add number

🔗 Result Handling — Chain Variables

Chain apply-mode variables to the output. Each variable receives the result of the previous one.

addDays()

+ Chain another variable

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Related Variables

Same category: Date

→ basicDateToExtended → calculateDaysDifference → calculateLeadTime → currentTimestamp → dateToUnixTimestamp → daysToMilliseconds → extendedDateToBasic → getDayIndexFromDateString → getDayName → getDayNameFromDateString → getDayNameShort → getHourOfDay → getMonthName → getMonthNameShort → hoursToMilliseconds → isBusinessHours → isWeekend → millisecondsToDays → millisecondsToHours → millisecondsToMinutes → millisecondsToSeconds → minutesToMilliseconds → reverseDateCompactDay1st → reverseDateCompactYear1st → reverseDateSlash → secondsToMilliseconds → subtractDays → timestampToDayIndex → unixTimestampToDate

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Under the Hood

📜 View Implementation Code

/**
* Adds a specific number of days to a target date string.
*
* @param {string} data.src - The starting date in YYYY-MM-DD format.
* @param {number|string} data.days - The number of days to add.
* @param {Function|string} [data.out] - Optional output handler.
*
* Direct-mode specific parameters:
* @param {Function} [data.pre] - Optional pre-processor function to transform src.
*
* @returns {string|undefined} The new date in YYYY-MM-DD format, or undefined if invalid.
*
* @framework ggLowCodeGTMKit
*/
const makeNumber = require('makeNumber');

const addDays = function(dateString, daysToAdd) {
    if (typeof dateString !== 'string') { return undefined; }

    var days = makeNumber(daysToAdd);
    if (days !== days) { days = 0; }

    var matchParts = dateString.match("^(\\d{4})-(\\d{2})-(\\d{2})$");
    if (matchParts === null) { return undefined; }

    var year = makeNumber(matchParts[1]);
    var month = makeNumber(matchParts[2]);
    var day = makeNumber(matchParts[3]);

    var isLeapYear = function(y) {
        return (y % 4 === 0 && y % 100 !== 0) || (y % 400 === 0);
    };

    var dateToAbsoluteDays = function(y, m, d) {
        if (y < 1900 || y > 2100) { return undefined; }
        if (m < 1 || m > 12) { return undefined; }

        var daysInMonth = [0, 31, isLeapYear(y) ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
        if (d < 1 || d > daysInMonth[m]) { return undefined; }

        var total = 0;
        var i = 1900;

        while (i < y) {
            total = total + (isLeapYear(i) ? 366 : 365);
            i = i + 1;
        }

        i = 1;
        while (i < m) {
            total = total + daysInMonth[i];
            i = i + 1;
        }

        return total + d;
    };

    var absoluteDaysToDate = function(absDays) {
        var y = 1900;
        var yearDays = isLeapYear(y) ? 366 : 365;

        while (absDays > yearDays) {
            absDays = absDays - yearDays;
            y = y + 1;
            yearDays = isLeapYear(y) ? 366 : 365;
        }

        var m = 1;
        var daysInMonth = [0, 31, isLeapYear(y) ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];

        while (absDays > daysInMonth[m]) {
            absDays = absDays - daysInMonth[m];
            m = m + 1;
        }

        var d = absDays;

        var mm = m < 10 ? '0' + m : '' + m;
        var dd = d < 10 ? '0' + d : '' + d;

        return y + '-' + mm + '-' + dd;
    };

    var absDays = dateToAbsoluteDays(year, month, day);
    if (absDays === undefined) { return undefined; }

    var newAbsDays = absDays + days;
    if (newAbsDays < 1) { return undefined; }

    return absoluteDaysToDate(newAbsDays);
};

const safeFunction = fn => typeof fn === 'function' ? fn : x => x;
const out = safeFunction(data.out);
// ===============================================================================
// addDays - Direct mode
// ===============================================================================
const applyCast = (castFn, value) => s

🧪 View Test Scenarios (7 tests)

✅ '[example] Add One Week'
✅ '[example] Cross Month Boundary'
✅ Cross Leap Year Boundary
✅ Cross Non-Leap Year Boundary
✅ Add 365 Days
✅ Add negative days
✅ Invalid date returns undefined